1. Field of the Invention
The present invention relates to a developing device for copiers and printers and the like, wherein an electrostatic latent image formed on an image-carrying member is developed by toner.
2. Description of the Related Art
A conventional developing device is shown in FIG. 10. In the developing device 1a, the developing roller 4 includes a rotatable sleeve 6 as an external housing installed over a non-rotating stationary magnet roller 5, and is accommodated in an open portion 3 formed in housing 2 confronting the photosensitive member 12, and a regulating member 7 is arranged opposite the sleeve 6 to provide a fine gap of predetermined size on the top exterior surface thereof. Magnetic poles S1, N1, S2, N2, S3, N3, S4 which extend in the axial direction are sequentially formed on the exterior circumference of the magnet roller 5 along the direction of rotation of said sleeve (clockwise direction in the drawing), such that the magnetic pole S1 is disposed opposite the regulating member 7, and magnetic pole S2 is disposed opposite the photosensitive member 12. Magnetic fields are formed on the exterior surface of the sleeve 6 via the aforesaid magnetic poles S1.about.S4, and the vertical magnetic force Br of said magnetic fields is distributed so as to peak above the center of said magnetic poles, respectively, as shown in FIG. 11. The reference label "G" in FIG. 11 refers to Gauss units of magnetic force, and is used throughout the following description.
In the developing device 1a of the previously mentioned construction, a developer 10, comprising a carrier and a toner accommodated in a developer reservoir 8, is supplied to the developing roller 4 via the supply roller 9. The developer 10 supplied to the developing roller 4 is maintained on the exterior surface of the sleeve 6 by means of the magnetic force of the magnetic pole S1. The developer 10 is transported in a clockwise direction in conjunction with the rotation of the developing sleeve 6, and after the amount of transported toner is adjusted by means of the regulating member 7, said toner is supplied to the electrostatic latent image formed on the surface of the photosensitive member 12 in the area confronting said photosensitive member 12, thereby rendering the image visible. The developer 10 which passes the area opposite the photosensitive member 12 continues to be transported in a clockwise direction, and is released from the magnetic force of the magnet roller 5 at a location past the area opposite the magnetic pole S4, whereupon said toner is collected in the developer reservoir 8. On the other hand, the toner which was supplied to the photosensitive member 12 is transferred onto a transfer member such as a paper sheet or the like at a transfer area not shown in the illustration, thereby forming an image thereon.
Another well known developing device is shown in FIG. 12. In the developing device 1b, magnetic poles S1, N1, N2, S2, N3, N4, S3 are sequentially formed on the exterior circumference of the magnet roller 5 along the direction of rotation of said sleeve, such that the magnetic pole S1 is disposed opposite the regulating member 7, and magnetic pole S2 is disposed opposite the photosensitive member 12, and magnetic poles N1 and N2 having the same polarities are arranged medially to said magnetic poles S1 and S2. Furthermore, magnetic fields are formed on the exterior surface of the sleeve 6 via the aforesaid magnetic poles S1.about.S3, and the vertical magnetic force Br of said magnetic fields is distributed as shown in FIG. 13. In other respects the construction of the present device is identical to that of the previously described developing device 1a, and, therefore, like parts are designated by like reference numbers and further description is omitted.
In the developing device 1b, after the amount of the developer 10 which has been supplied to the sleeve 6 is adjusted by means of the regulating member 7, and when said developer 10 arrives at the area opposite the magnetic pole N1, it is regulated by a repulsive magnetic field (refer to FIG. 14) formed by the magnetic poles N1 and N2, such that a collection of developer 10 is formed in the area opposite the magnetic pole N1. The collected developer 10 is pushed out by subsequently transported developer 10, becomes airborne in the area confronting the magnetic pole N2, and is again maintained on the surface of the sleeve 6 so as to be transported in a clockwise direction (refer to FIG. 15). The developer 10 is disturbed at the aforesaid collecting area, and not only travels in the direction of rotation of the sleeve 6, but also travels in the axial direction of said sleeve 6. Accordingly, when foreign particles congregate in the gap formed between the sleeve 6 and the regulating member 7 such that areas lacking developer 10 are produced on the surface of the sleeve 6, the developer on the periphery of the previously mentioned collection of developer 10 is supplied to said areas lacking developer 10, thereby eliminating said areas lacking developer 10 and preventing white streaks on the image.
However, the developing device 1a has certain disadvantages inasmuch as when large diameter foreign particles such as toner clumps, masses and the like contained in the developer 10 become lodged between the sleeve 6 and the regulating member 7, said foreign matter excludes the developer 10, such that white streaks caused by a lack of adhered toner appear on those portions of the image at corresponding locations.
Furthermore, the developing device 1b has certain disadvantages inasmuch as the developer 10 is airborne between the area confronting the magnetic pole N1 and the area confronting the magnetic pole N2, such that some of the airborne developer 10 is dispersed in the vicinity, whereupon said dispersed developer 10 may adhere to the surface of the photosensitive member 12, thereby producing fog on the image and soiling the surrounding components.